With an increasing demand for making it easy and automated to operate a driving apparatus, such as an automotive vehicle, a transmission system has been automated, and a constant-speed cruise control system for enabling the driving apparatus to travel at a constant speed has been developed.
In general, the cruise control system performs constant-speed cruise control by setting a target vehicle speed to a vehicle speed detected at the time when a cruise control set switch is turned on, and controlling the vehicle so as to maintain the target vehicle speed.
Since a gear position or shift position of the transmission needs to be changed in some cases so as to keep the vehicle running at a constant speed, the cruise control system is required not only to control the engine output, but also control changes of the gear position of the transmission. To this end, the cruise control system is provided with an automatic shift device for changing the gear position to the one suitable for the current vehicle running condition, so as to maintain the target vehicle speed.
The cruise control device, as described above, is also adapted to cancel constant-speed cruise control when the driver steps on a footbrake or brake pedal, for example
In the conventional cruise control system, as described above, however, the constant-speed cruise control is not canceled when the driver selects a manual shift mode, and manually carry out a shifting operation. For example, the vehicle speed preset for the cruise control is undesirably maintained even where the driver manipulates a change lever so as to shift down the transmission so that the vehicle speed is reduced due to an effect of an engine brake.
In view of the above problem, Japanese laid-open Patent Publication No. 8-193656 discloses a technique for ignoring a shift command from a cruise control ECU when the manual shift mode is selected in an automatic transmission equipped with a manual shifting function. the manual shift mode is selected, however, only the shift command generated under the cruise control is ignored, and constant-speed cruise control is still continued or maintained, and therefore the vehicle speed cannot be reduced unless the brake pedal is depressed by the driver so that the cruise control is canceled.
Namely, if the constant-speed cruise control is kept effective even after the manual shift mode is selected and a shift command for upshifting or downshifting is generated, the vehicle speed preset for the cruise control is maintained even where the driver attempts to reduce the vehicle speed only by use of the engine brake, by shifting down the transmission without using the brake pedal. In this case, the vehicle speed cannot be reduced as desired.